The present disclosure relates to subject matter contained in priority Japanese Patent Application No. 2001-46052, filed on Feb. 22, 2001, the contents of which is herein expressly incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a high frequency power source, a plasma processing apparatus, an inspection method for a plasma processing apparatus, and a plasma processing method used for manufacturing electronic devices such as semiconductors and liquid crystal display devices, and micro electro-mechanical systems.
2. Description of Related Art
The importance of a thin film machining technology by means of plasma processing is increasing in manufacturing electronic devices such as semiconductors and liquid crystal display devices, and micro electro-mechanical systems.
Plasma processing using a patch antenna type plasma source will be described below as an example of a conventional plasma processing. A predetermined gas is introduced into a vacuum chamber from a gas supplying device while an evacuation device evacuates the vacuum chamber to maintain the inside of the vacuum chamber at a predetermined pressure. A high frequency power source for an antenna supplies an antenna provided protrudingly in the vacuum chamber with a high frequency power with a frequency (f) of 100 MHz. Consequently plasma is generated in the vacuum chamber, and a plasma processing operation is performed to a substrate placed on an electrode placed in the vacuum chamber.
FIG. 5 shows a detailed view of a high frequency power source 104 for an antenna. An amplifier 23 amplifies a signal with a high frequency (f) of 100 MHz generated from a high frequency oscillator 22, and a high frequency output terminal 25 provides a high frequency power through a directional coupler 24. When the amplifier 23 amplifies the signal from the high frequency oscillator 22, a signal from a traveling wave output terminal 26 of the directional coupler 24, and a signal from an output power setting circuit 31 are compared with each other to provide a constant high frequency power. A power indicator 30 is provided to show a traveling wave power and a reflected wave power based on a signal from the traveling wave output terminal 26, and a signal from a reflected wave output terminal 28 of the directional coupler 24.
A matching circuit 20 shown in FIG. 6 is provided to match the impedance of the antenna with the characteristic impedance of a coaxial line.
However, there is a problem that precise power control and precise power monitoring are not available in the plasma processing of prior art. When a load is linear, a harmonic wave is not generated on a power system from the high frequency power source 104 to the load. When a load with strong non-linearity such as plasma is used, a harmonic wave is generated on the load. Because the high frequency power source 104, and the matching circuit 20 match the frequency (f) of the oscillator 22, and do not match a higher harmonic wave with a frequency such as 2f, 3f, and 4f, there are standing waves, which are higher harmonic waves, on the power system from the high frequency power source 104 to a load. Thus, when a state of a load, plasma generating conditions such as the kind of the gas, a flow rate of the gas, the pressure, and the high frequency power, the length of the coaxial line, and a deposit state of the inner wall of the vacuum chamber change the locations of nodes and antinodes of the standing waves as well as the amplitudes of the generated higher harmonic waves change. Consequently, a ratio of a higher harmonic wave component to a fundamental wave component contained in the signal from the traveling wave output terminal 26 of the directional coupler 24 changes. As a result, a gain of the amplifier 23 changes, a fundamental wave power destabilized, and the power cannot be controlled precisely. Simultaneously, a power value shown on the power indicator 30 includes the harmonic waves, and the fundamental wave power cannot be precisely monitored.
When the high frequency power is measured in an inspection for a plasma processing apparatus as shown in FIG. 6, if a directional coupler 32 for inspection provided with a traveling wave output terminal 33 for inspection, and a reflected wave output terminal 34 for inspection is provided on a coaxial line 21, because it is impossible to precisely monitor the power due to the effect from the standing waves of the higher harmonic waves, the plasma processing apparatus is not precisely inspected.
For example, when plasma was generated immediately after a wet maintenance of the vacuum chamber while an argon gas flow rate was 100 sccm, and a high frequency power was 1500 W, and the pressure changed from 0.3 to 2 Pa, the value of the high frequency power measured by the directional coupler 32 for inspection presented a variation from 1400 W to 1540 W, which is a deviation of plus or minus 4.8 percent from 1470 W.
In light of the foregoing, an object of the present invention is to provide a high frequency power source, a plasma processing apparatus, and a plasma processing method for precise power control, and an inspection method for precise power monitoring.
A high frequency power source according to a first aspect of the present invention includes a high frequency oscillator, an amplifier, a directional coupler provided with a traveling wave output terminal and a reflected wave output terminal, a high frequency wave output terminal, and an output power setting circuit. In this high frequency power source thus constituted, a signal from the traveling wave output terminal, and a signal from the output power setting circuit are compared to provide a constant high frequency power from the high frequency wave output terminal when the amplifier amplifies a signal from the high frequency oscillator, and a low pass filter with a cut-off frequency (fh) higher than an oscillating frequency (f) of the high frequency oscillator is provided between the traveling wave output terminal and the amplifier.
A plasma processing apparatus according to a second aspect of the invention includes a vacuum chamber, a gas supplying device for supplying the vacuum chamber with gas, an evacuation device for evacuating the vacuum chamber, an electrode for placing a substrate in the vacuum chamber, an antenna provided so as to face the electrode, a high frequency power source for providing the antenna or the electrode with a high frequency power with a frequency of (f), a matching circuit, and a coaxial line for connecting the high frequency power source with the matching circuit, wherein a low pass filter is provided between a traveling wave output terminal and an amplifier in the high frequency power source.
An inspection method for a plasma processing apparatus according to a third aspect of the invention is an inspection method for a plasma processing apparatus comprising a vacuum chamber, a gas supplying device for supplying the vacuum chamber with gas, an evacuation device for evacuating the vacuum chamber, an electrode for placing a substrate in the vacuum chamber, an antenna provided so as to face the electrode, a high frequency power source for providing the antenna or the electrode with a high frequency power with a frequency of (f), a matching circuit, and a coaxial line for connecting the high frequency power source with the matching circuit, where the high frequency power source is provided with a low pass filter, and a high frequency power passing through the coaxial line is measured while a directional coupler for inspection provided with a traveling wave output terminal for inspection and a reflected wave output terminal for inspection is provided on the coaxial line, and the low pass filter with a cut-off frequency (fk) higher than an oscillating frequency (f) of a high frequency oscillator is provided between the traveling wave output terminal for inspection and a power measuring device for inspection.
A plasma processing method according to a forth aspect of the invention includes the procedures of controlling an inside of a vacuum chamber at a predetermined pressure while the vacuum chamber is being supplied with gas, and is simultaneously being evacuated, applying a high frequency power with a frequency (f) to an electrode or an antenna facing a substrate placed on the electrode in the vacuum chamber through a coaxial line and a matching circuit, and generating plasma inside the vacuum chamber to process the substrate. In this method, when a signal from a high frequency oscillator is amplified in an amplifier in a high frequency power source, a signal from a traveling wave output terminal of a directional coupler in the high frequency power source through a low pass filter with a cut-off frequency (fh) higher than an oscillating frequency (f) of the high frequency oscillator is compared with a signal from an output power setting circuit in the high frequency power source to apply a constant high frequency power to process the substrate.
While novel features of the invention are set forth in the preceding, the invention, both as to organization and content, can be further understood and appreciated, along with other objects and features thereof, from the following detailed description and examples when taken in conjunction with the attached drawings.